fix: clean rewrite of audio recovery matching Kima Hub design

playCurrent():
- Remove canplay listener from before play() — it caused a race where
  both the listener and the initial play() fired simultaneously
- canplay is now only registered in the catch (failure path only),
  eliminating the double-play race entirely
- AbortError: reload src+load() with _trackChanging=true (OS interruption
  recovery); canplay fires once buffered and retries play()
- Other errors: reset _trackChanging, let canplay retry (not throttled
  by Android background timers unlike setTimeout)
- Add 10s safety net to reset _trackChanging if Doze kills everything
  (matches Kima Hub's reload failsafe)

main.js error handler:
- Skip when _trackChanging=true (playCurrent already recovering) to
  prevent conflicting dual recovery attempts
- _onForeground: reset _trackChanging on play() failure so the flag
  can't get stuck when foreground recovery also fails

index.html:
- Add crossorigin=anonymous: Navidrome and NovaSonic backend both send
  Access-Control-Allow-Origin:* so this is safe, and it enables proper
  cross-context HTTP caching for cover art and audio responses

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

index.html

@@ -590,7 +590,7 @@
 <div class="jobs-panel" id="jobs-panel"></div>
 
 <div class="toast-container" id="toast-container"></div>
-<audio id="audio-element" preload="auto" playsinline></audio>
+<audio id="audio-element" preload="auto" playsinline crossorigin="anonymous"></audio>
 <audio id="preview-audio"></audio>
 <audio id="abs-audio"></audio>